The 15-page suit, filed today in State Supreme Court, asks for the city to be barred from proposing changes to how school buildings are used that would take effect after the first day of the following school year. The suit comes as the Department of Education considers plans, including charter school co-locations, that would not be implemented until 2015, nearly two years after Mayor Bloomberg leaves office.

If a judge sides with the union, the department could try to set co-locations for the fall of 2014 this fall, but it could not plan further ahead, and plans that were approved last year for 2014 would be undone.

Union officials will review any plans the department proposes this fall but based the lawsuit on what it already did, according to a spokeswoman. The lawsuit names 16 plans that the Panel for Educational Policy has already approved that the union says represent an inappropriate form of planning ahead.

Most of those plans clear the way for charter schools to operate in district school buildings, a Bloomberg administration practice that has allowed the charter sector to flourish.

James Merriman, CEO of the New York City Charter School Center, said in an interview that he thought the lawsuit signaled that UFT President Michael Mulgrew is not sure that the union’s mayoral candidate, Bill Thompson, will prevail.

“The next mayor who comes in will have the same power and latitudes and control of the system that mayoral control provides to this mayor,” Merriman said. “I think the UFT stepping in and trying a court suit just shows that they’re not very confident, nor should they be, that the [new] mayor is going to roll back any of these things.”

Chalkbeat New York

Stay on top of New York education news with our morning newsletter.

“I didn’t even know what I was missing, but as soon as Chalkbeat’s info started rolling in, it was like a part of my brain just started lighting up. You need what they have to offer.” — Tim L.

Other advocates said the lawsuit fit into a union pattern and vowed to fight it.

“We’ve seen the UFT go to court to keep families stuck on school waiting lists and prevent new schools from opening, and they’ve failed,” said Jeremiah Kittredge, executive director of Families for Excellent Schools, in a statement.

While the union’s legal efforts to block charter school co-locations in the past have been dismissed, the union has successfully blocked the Department of Education from carrying out changes to schools multiple times. In 2010, the union convinced a judge to halt the city’s school closure plans because the city had not correctly completed its Education Impact Statements, and last year, an arbitrator reversed the department’s “turnaround” plans over labor issues, effectively blocking the closure and creation of dozens of schools.

“With this lawsuit, the UFT is telling the tens of thousands of parents looking for a better option for their children that the doors of public school buildings are closed to them,” said Glen Weiner, interim executive director of StudentsFirstNY, in a statement. “We will do everything in our power to ensure that the judicial process is informed by the view of parents who do not want to see the clock rolled back on their kids.”